Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 34 to 38.       Psychologists have long known that having a set of cherished companions is crucial to mental well-being. A recent study by Australian investigators concluded that our friends even help to prolong our lives. The study concentrated (34) ______ the social environment, general health, and lifestyle of 1,477 persons older than 70 years. The participants were asked how (35)______ contact they had with friends, children, relatives and acquaintances. Researchers were surprised to learn that friendships increased life (36) ______ to a far greater extent than frequent contact with children and other relatives. This benefit held true even after these friends had moved away to another city and was independent of factors such as socioeconomic status, health, and way of life. According to scientists, the ability to have relationships with people to (37) ______ one is important has a positive effect on physical and mental health. Stress and tendency towards depression are reduced, and behaviours that are damaging to health, such as smoking and drinking, occur less frequently. (38)_______, our support networks, in times of calamity in particular, can raise our moods and feelings of self-worth and offer helpful strategies for dealing with difficult personal challenges. (Source: Academic Vocabulary in Use by Michael McCarthy and Felicity O’Dell)

The study concentrated (34) ______ the social environment, general health, and lifestyle of 1,477 persons older than 70 years.